I remember about a year ago, the chairman of the GOP saying that they had a deep field of candidate for the 2016 presidential election; and then Donald Trump thru his hat in the ring...We are now in April 2016, and within the next few weeks (maybe days) the presumtive nominees for the Democrats and the Republican will be finalizes. Ms Clinton with all her faults, real, perceived or simply made up, will almost certainly head up the Democrats. For the GOP its still a choice between Trump and Cruz, but in reality neither are acceptable to the vast majority of the electorate -- so it really doesn't matter.
What is truly interesting is the impact on November's voters; some will vote only the down ticket, but in reality voters almost never vote the bottom of the ticket. So my best guess is that a lot of Republicans will stay home in November, will hand the Democrats a victory on par with what Reagan got in the 1980's a 30/40 state victory -- this will be a historic defeat for the GOP; if its Trump (which is looking increasingly likely) the GOP will be able to say that it was not them, it was the nominee's fault -- giving them the ability to further deny reality of their failed policy, if its Cruz, I suspect they will still say its the candidate, but they will not be able to say that he was not at the very very right end of the spectrum.
This will at the very least hand the Senate back to the Democrats -- and may do the same for the house...although the house is, with all its gerrymandering, is harder to judge.
Maybe the GOP will change its ways. The rise of Trump is entirely due to the GOP's historical habit of bait and switch; talk about values and middle america as the core of the economy, but then pass legislation that allows the 1% to off-shore their wage bill to lower cost jurisdiction and cut the 1% taxes even further. In short the GOP has largely taken its voters for granted (BTW the Democrats have done the same with the african american vote too...), still Trump has clearly addressed these "core Americans' concerns" (e.g. middle age blue collar white guys). The press loves Trump, he gets about 85% of all press coverage. His rallies are energies (and apparently violent).
The GOP's conundrum is as follows: After the 2012 defeat the GOP undertook a full review of its platform and what Americans were saying -- especially Republican Americans; and instead of following the script (Jeb Bush by the way) the GOP went full loco, full right wing crazy -- build a wall etc etc etc. Granted the GOPs problem are even deeper; their willingness to gerrymander certain congressional seats means that there is an increasingly large number of representants that will not move an inch from their dogmatic position -- because they don't need to! They are elected by a minuscule subset of the electorate (in primaries) and then always win! The GOP has no control on the selection process -- since all these campaigns are self funded (BTW that's what gave rise to Mr. Trump)
That's the GOP conundrum, the two front runners for the nominations are both deeply flawed candidates that the GOP establishment will easily dismiss as irrelevant; making the GOP unelectable for the foreseeable future. Now I am not a republican (for starts I am not an American), still any political system who has a broken party is pray to massive problems. The UK faced similar situation during the Thatcher years -- the labour party was unelectable, and so the system of check and balances fell apart.